1. Field of the Invention
The present invention relates to a thermoplastic elastomer composition having characteristics capable of repeating formation of crosslinking and dissociation of crosslinking with temperature change (hereinafter, also simply referred to as “recycle property”). In particular, the present invention relates to a thermoplastic elastomer composition having excellent mechanical characteristics and compression set (shape retention), without impairing an excellent recycle property.
2. Description of the Related Arts
In recent years, reusage of waste materials is desired in view of environmental protection and resource saving. Vulcanized rubbers have stable three-dimensional networks in which polymer chain and vulcanizing agent are covalently bonded, and therefore show very strong strength, but are difficult to re-mold and reuse due to strongly covalent bond crosslinking. On the other hand, thermoplastic elastomers utilizing physical crosslinking state do not require complicated vulcanization and molding steps including pre-molding and the like, and therefore can easily be molded by heat melting.
Thermoplastic elastomer comprising a resin component and a rubber component, in which a crystaline resin component forms a hard segment which serves as crosslinking part of a three-dimensional structure at room temperature to thereby prevent thermoplastic deformation of a rubber component (soft segment) whereby the thermoplastic elastomer plastically deforms by softening or fusion of the resin component with rising a temperature, is known as the representative example of such thermoplastic elastomers. However, such type of thermoplastic elastomers is liable to decrease rubber elasticity because of containing a resin component. For this reason, materials that do not contain a resin component and can impart thermoplasticity are demanded.
To solve the above problem, the inventors of the present invention previously proposed that an elastomer composition comprising an elastomer having a reaction site capable of forming hydrogen bonds and a compound having a reaction site capable of forming hydrogen bond together with the reaction site of the elastomer can repeats formation of crosslinking and dissociation of crosslinking by temperature difference utilizing hydrogen bond (JP 11-209524 A). Further, the inventors of the present invention proposed a hydrogen-bonding thermoplastic elastomer comprising an elastomeric polymer having a carbonyl-containing group and a heterocyclic amine-containing group in side chains, which is expected to have the similar effect (JP 2000-169527 A). JP 8-239583 A describes metal-containing organic polymer material containing compounds having specified metal elements and organic polymers having a carbonyl-containing group and a nitrogen-containing heterocycle-containing group in side chains, wherein the nitrogen-containing heterocycle-containing ring-containing group is bonded to the main chain directly or through an organic group at a 2-position counted from the nitrogen atom.
Those elastomer compositions or metal-containing organic polymer materials can sufficiently show melt flowability at a molding temperature of a thermoplastic resin such as olefin-based resin without modification, have excellent mechanical strength (breaking strength) at low temperature by the formation of crosslinking, and are capable of repeated reformation of crosslinking and dissociation of crosslinking (softening).
Thermoplastic elastomers having such properties have very high value on industrial utilization and also very high value on environmental protection and are expected for use as a material having further high crosslinking strength and having excellent recycle property, showing no change in physical properties even if formation of crosslinking and dissociation of crosslinking are repeated.
Incidentally, the above-mentioned thermoplastic elastomer (composition) or a metal-containing organic polymer material, with respect to material characteristics thereof, may have insufficient shape retention after loading and insufficient compression set at the time of unloading after loading for a predetermined time period.
Further, metal-containing organic polymer material described in JP 8-239583 A have had the problems such that strength is very small, and the properties are insufficient in using as an elastic material, such as using as a rubber material.